Deployer is an amazing tool that is used to deploy websites (hence the name). I have looked at other tools, but because Deployer is built and run using PHP, using it to deploy PHP sites makes sense. It also means that I don't have to figure out complex XML documents or learn Ruby just to understand what the deployment is doing.
I have been using Deployer for a little while now to deploy my own site but I have been using the root user to accoumplish the deployments to get around any permissions issues. When I sat down with the developers at work we looked into how to setup the server so that deployments could be run without giving the tool unfettered access to the server. To this end we set out a plan to create a 'deployer' user on our servers that would be the user Deployer uses to deploy sites.